Compressed air is frequently used by workmen and others for purposes of cleaning or dusting the work areas, materials, or machines with which they are working. Typically, a source of pressurized air is tapped by the workman, and the compressed air is conveyed through flexible hoses to the work area. A manually operable air gun or some similar device is connected to the flexible hose so that the pressurized air can be selectively directed at the object requiring cleaning or dusting. The use of the compressed air in this manner provides an effective and efficient means for removing foreign and unnecessary material from the work area. When blown with the compressed air, small particles, dirt and other unwanted material tend to fly off of the targeted object so as to leave the work area relatively clean.
Workmen and others using compressed air for cleaning have also been known to engage in mischievous conduct which includes, among other practices, directing pressurized air at an individual. Particularly, injury has often resulted when the nozzle of an air gun is placed against the body of a person and pressurized air released from the gun. The high pressure air can penetrate the victim's skin, be admitted into his veins and blood vessels, and consequently result in serious injury and even death.
Partially as a result of the above circumstances, there has been promulgated under the Occupational Safety and Health Act a regulation that prohibits the use of compressed air for cleaning purposes except when reduced to less than 30 p.s.i. As explained in a later directive, the regulation was interpreted to mean that the downstream pressure of the air at the nozzle or opening of the air gun must be below 30 p.s.i. when the nozzle or opening is obstructed or dead ended. Thirty p.s.i. would not be sufficient pressure to result in injury to the victim when applied to his skin.
To meet these standards, there has previously been provided air guns which accept compressed air at a high pressure, but which deliver the compressed air within the 30 p.s.i. maximum limitation both during normal operation and when obstruction of the nozzle end occurs. Typically, this has been accomplished through the employment of certain structural features which either alone or in combination act to bleed off the pressurized air or allow for its commingling with ambient air. In each device, however, high pressure air, which is more desirable for cleaning, is not available.
For example, as illustrated in U.S. Pat. No. 3,263,934 to Hope, Jr., et al. and U.S. Pat. No. 3,129,892 to Tillman, air guns having nozzles with large expansion chambers have been proposed. Typically, the air gun includes an inner opening or orifice through which the pressurized air is emitted at a high velocity. Surrounding the orifice and projecting outwardly from the air gun body is positioned an outer tube within which is formed the expansion chamber and through which the stream of pressurized air must pass. Since the length of the expansion chamber between the orifice and the outlet of the outer tube is usually several times its diameter, the stream of compressed air is afforded a large volume into which it can expand. Consequently, the velocity of the compressed air between the orifice and the outlet end is severely reduced, diminishing the concentration of the directed stream of air and permitting substantial diffusion immediately upon exit of the compressed air from the outlet end.
Often in combination with the expansion chamber is included apertures or vent holes in the wall of the outer tube and forward of the orifice, as shown in the above noted patents to Hope, Jr., et al. and Tillman. The vent holes are provided for purposes of releasing the internal pressurized air in the event the outlet end is obstructed. However, the vent holes also have the effect of reducing the air pressure during normal operation prior to emission from the outlet end. Ambient air is drawn into the nozzle through the vent holes by the flow of the pressurized air through the outer tube. As the ambient air mixes with the pressurized air, the resulting usable air pressure is below that originally provided to the air gun.
Another method by which the air pressure is reduced before emission from the air gun is illustrated in U.S. Pat. No. 3,790,085 to Ayer and U.S. Pat. No. 3,599,876 to Kyburg. This design provides air passages which communicate with the flow of compressed air prior to emission of the compressed air from the inner opening or orifice of the air gun. These air passages are provided to prevent a build-up of air pressure in the nozzle in the event the outlet end of the nozzle is obstructed. Again, however, the air pressure provided originally to the air gun is not delivered to the work area. Pressurized air is allowed to escape through the air passages or ambient air is allowed to mix with the pressurized air so that even before the air reaches the orifice, the air pressure is lowered.